AWS Characteristics

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Characteristics of the AWS to be

Parameter Source Data Format AWS I/O Remark Optional / Mandatory
Position GPS NMEA (RMC) serial input From ships system or own sensor Mandatory
Time GPS NMEA (RMC) serial input From ships system or own sensor Mandatory
Course, Speed GPS NMEA (RMC) serial input From ships system or own sensor Mandatory if wind sensor connected to AWS
Heading Compass / Gyro NMEA (HDT) serial input From ships system or own sensor Depending on quality required
see notes below
Pressure Barometer
i.e. PTB330, PTU300,...
proprietary telegram serial input Height of Barometer required Mandatory
Sea Surface Temperature Thermometer
typically PT100
foil or weld-in plunger
Resistance serial input
(converter required)
Probably needs to be polled Optional
(due to complex cabling)
Wind Ultrasonic Anemometer
i.e. Gill, Thies,...
NMEA (MWV) serial input Heading, Speed and Course of vessel required for calculation of true wind Basic AWS: Optional
Complex AWS: Mandatory
Temperature Thermometer
typically PT100
i.e. HMP45D, LTS2000,...
Resistance serial input
(converter required)
Can be connected to PTU-sensor if available Basic AWS: Optional
Complex AWS: Mandatory
Humidity Humicap
i.e. HMP45D
Voltage serial input
(converter required)
Can be connected to PTU-sensor if available Basic AWS: Optional
Complex AWS: Mandatory
Display-Unit AWS internal calculations Input via Human-Interface-Device
i.e. Keyboard, Mouse,...
link Display-Unit <-> AWS
(serial or network)
could be AWS itself Optional, unless Visual Observations wanted
Wind-Display
relative Wind-Data NMEA serial output possibly connected directly to sensor Optional
Visual Observation Human Observer Input via Human-Interface-Device
i.e. Keyboard, Mouse,...
link Display-Unit <-> AWS
(serial or network)
If wanted: Display Unit mandatory Optional, unless wanted by Operator of complex AWS
Optional sensors Depending on requirements proprietary telegram serial input(s) i.e. Radiation, Visibility, Thermosalinometer, Cloud Height, Preciptiation,... Optional
Weather report
AWS internal calculations Dataformat specified by Operator serial output or network FM-12, FM-13,...
various types of transmitter
Mandatory
Data Output
AWS internal calculations proprietary NMEA serial output or network with timestamp Mandatory if connected to ships scientific system
Data Storage
AWS internal calculations i.e. IMMT, VOS-Clim,... internal file that can be downladed
i.e. via USB
Requirement or not?
data from which period of time?
Status pending


Further topics that might need to be considered

  • Supply Voltage - possibly 10-30VDC?
  • Power comsumption - any restrictions here?
  • Size of the system - any restrictions here?
  • Temperature Range - standard / extended?
  • Anyone needing sensors port- and starbord?
  • Calculation of True Wind - What quality is required here? - Please see notes below


Calculation of True Wind

If looking onto a system that is as independent from the ship as possible, a connection to the ships system is not applicable. This leads to two possible solutions:

  • The Usage of an own GPS and an own compass (or a GPS compass) - better quality but higher price
  • The Usage of only a standard GPS - less quality but lower price

Reasons leading two these options (with examples from DWD):

The True Wind gets calculated from two vectors: One is the relative Wind, delivered by the sensor. The other one is the movement of the ship (course and speed).
An ordinary GPS (only one receiver) calculates the course over ground and the speed over ground from the deviation between the present position and the previous position. It assumes that the ship sails straight forward from one point to another.
If the vessel i.e. drifts sideways, or even worse sails backwards, the calculation would be wrong. The error is typically not very big, but with strong currents and low speeds, the error could be noticable.
Old DWD systems (mainly used on merchant vessels) used only an one-receiver GPS, and didn't calculate the true wind when slower than roughly 3kn. For merchant vessels that was fine, but for coast guard and research vessels that was not sufficient, since these vessels tend to drift quite a lot, and especially since scientists onboard of research vessels needed permanently the true wind.
To get a proper calculation, DWD is now always using data from a compass. By this the system knows always where the bow is pointing to. This information is combined with the relative wind to get the correct vector needed for the calculations. The other vector is still the movement of the vessel.

If using a magnetic compass, there will of course be an error due to the magnetic deviation. That's why DWD is now using - if possible - GPS compasses (GPS with more than one receiver). Those systems are strictly north seeking.

Of course there is only the need of one connection to a GPS and one connection to a compass. In the case of the standard DWD AWS all required data (RMC and HDT) gets delivered via one serial link from the ships system. When there is a GPS compass installed, it delivers exactly those required data.